AU
B171E-00

DTC B171E-00 indicates the driver-side knee airbag ignition circuit resistance exceeds the normal threshold range (typically 1 — Qin Plus

Safety System

DTC B171E-00 indicates the driver-side knee airbag ignition circuit resistance exceeds the normal threshold range (typically 1.5Ω-3.5Ω, depending on vehicle calibration) established by the SRS control module (ACU), registering as excessively high resistance.

Potential causes include increased internal resistance in the airbag inflator, poor wiring harness connector contact, a wiring harness open or short circuit, or a faulty internal sampling circuit within the control module.

This fault forces the SRS system into a degraded mode and illuminates the instrument panel airbag warning light.

During a collision, the knee airbag may fail to deploy, compromising lower limb protection for the driver.

5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Aging or moisture ingress causes the knee airbag igniter internal resistance to drift beyond the normal range.
  • 2Airbag wiring harness connector (usually located under the left side of the dashboard, yellow plug): terminals oxidized, loose, backed out, or corroded by water ingress.
  • 3Knee airbag wiring harness worn, broken, or pinched inside the instrument panel, reducing the effective conductive cross-sectional area.
  • 4Liquid ingress into the airbag connector during vehicle wading or interior cleaning, causing increased contact resistance.
  • 5Internal resistance sampling circuit fault in the SRS control module (ACU) or abnormal software calibration causing a false alarm.
What To Do
  • 1
    Use BYD VDS or a dedicated diagnostic tool to read and confirm DTC B171E-00, record freeze frame data, and check the instrument panel airbag warning light status.
  • 2
    Disconnect the battery negative terminal and wait at least 3 minutes to fully discharge the SRS system and prevent accidental airbag deployment.
  • 3
    Remove the driver-side lower dashboard trim panel and locate the left knee airbag wiring harness connector (yellow plug, usually with a shorting bar). Inspect the connector for damage, water ingress, oxidation, or burn marks.
  • 4
    Disconnect the airbag connector. Use a digital multimeter to measure the resistance between the two terminals of the knee airbag igniter (standard value: approximately 2.0-3.0 Ω). If the resistance is >3.5 Ω or unstable, the airbag assembly is faulty.
  • 5
    Check wiring harness continuity between the connector and the ACU. Measure the wiring harness resistance (must be <1Ω) and insulation resistance to ground (must be >1MΩ). Inspect for high resistance or intermittent open circuits.
  • 6
    Check the connector pins for oxidation, backing out, or deformation. If necessary, clean with electrical contact cleaner, repair the pins, or replace the wiring harness.
  • 7
    Reconnect all connectors and confirm the locking tabs are fully engaged. Reconnect the battery negative terminal. Use the diagnostic tool to clear the fault code and perform the SRS system self-test (KOEO and KOER tests).
  • 8
    Perform a simulated crash sensor test (if supported) and confirm the knee airbag circuit status displays 'Normal' and no fault code recurs.
Real-World Cases
BYD DTC AI Analysis

Oxidation on wiring harness connector pins increased contact resistance

✓
A 2017 Qin EV300 with 80,000 km had a constant airbag warning light on the instrument cluster. A scan tool read DTC B171E-00. Removing the trim beneath the driver's side dashboard revealed obvious white oxidation on the internal pins of the yellow knee airbag harness connector. Contact resistance measured 5.2 Ω. We cleaned the pins thoroughly with electronic cleaner, applied conductive paste to prevent further oxidation, and reconnected the connector securely. The resistance returned to 2.1 Ω. After clearing the fault code, the system returned to normal.
BYD DTC AI Analysis

Knee airbag internal igniter resistance drift due to aging

✓
A 2017 Qin 100 with 120,000 km had an intermittent airbag warning light and sporadic DTC B171E-00. Repeated measurements showed the knee airbag resistance fluctuating irregularly between 2.8-4.5Ω, indicating an aging internal igniter causing unstable resistance. Replaced the driver-side knee airbag assembly (part number matched to VIN) after removing the lower dashboard trim panel. After installation, performed SRS system configuration and calibration using VDS. This completely resolved the fault.
BYD DTC AI Analysis

Connector water ingress and corrosion after wading

✓
A 2018 Qin EV450 showed an airbag warning light after driving in heavy rain, storing DTC B171E-00. Inspection found the driver's floor mat damp, obvious water stains inside the knee airbag harness connector, and green corrosion on the copper pins, increasing contact resistance to over 6Ω. Thoroughly cleaned and dried the harness connector, measured airbag resistance normal at 2.0Ω, also checked body seals and drain holes, and repaired the air conditioning intake seal to prevent further water ingress.
BYD DTC AI Analysis

Connector loose after unqualified repair

✓
A 2017 BYD Qin 80. The airbag light came on after the owner replaced the cabin filter. Inspection found the knee airbag connector (located near the cabin filter) hadn't been fully inserted, and its locking tab wasn't engaged, causing poor terminal contact and high resistance. Re-seated the connector until it clicked into place, cleared the DTCs with a scan tool, and the SRS self-test passed. Only qualified technicians should perform airbag repairs.
BYD DTC AI Analysis

SRS control module internal sampling circuit fault

✓
A Qin EV300 repeatedly logged fault code B171E-00 even though the left knee airbag resistance measured 2.1Ω (normal) on multiple tests. Wiring harness continuity and insulation were both good, and connectors showed no faults. Other circuits also triggered intermittent false alarms. Diagnosed as an internal resistance sampling circuit or A/D converter fault in the SRS control module (ACU). Replaced the airbag control module (ensure the replacement part number matches or is compatible with the original). After module coding, VIN writing, and system configuration, the fault was completely resolved.
Other Qin Plus Fault Codes
B1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.